Coral Disease, Environmental Drivers, and the Balance Between Coral and Microbial Associates

Abstract

across the globe, we are witnessing the decline of coral reef ecosystems. One relatively new factor contributing to this decline is the outbreak of destructive infectious diseases, especially on Caribbean reefs. As the Coral Disease Working Group of the Coral Reef Targeted Research Program, our research focuses on four priorities: (1) assessing the global prevalence of coral disease, (2) investigating the environmental drivers of disease, (3) identifying the pathogens that cause disease, and (4) evaluating the coral’s ability to resist disease. Monitoring has revealed new coral-disease syndromes at each of four Global Environmental Fund Centers of Excellence: the Caribbean, the Philippines, Australia, and East Africa. Over the last 20 years, drastic (> 50 percent) loss of coral cover has occurred on the Yucatán Peninsula, even in pristine areas. Global surveys have revealed significant levels of disease and disease outbreaks occurring not only in the Caribbean “hotspots,” but also in sites throughout the Pacific and Indian Oceans. By monitoring coral disease, we will create a baseline and long-term data set that can be used to test specific hypotheses about how climate and anthropogenic drivers, such as decreasing water quality, threaten coral reef sustainability. One such hypothesis is that high-temperature anomalies drive outbreaks of disease by hindering the coral’s ability to fi ght infection and by increasing the pathogens’ virulence. We observed recurrent outbreaks following the warm summer months of two of the most damaging diseases in the Caribbean. In addition, we found that coral disease in the Great Barrier Reef correlated with warm temperature anomalies. In the Caribbean and Mediterranean Seas, virulence of known coral pathogens and the normal coral flora changed during high-temperature periods. Other stresses such as high nutrients and sedimentation may similarly alter the balance between the coral and its resident microbial flora.